1. Field of the Invention
The present invention relates to an inverter apparatus for converting DC electric power into AC electric power, and a solar power generation apparatus using such inverter apparatus and, more particularly, to an inverter apparatus which has two modes, i.e., a tie operation mode with a main AC power system such as a commercial AC power system, and a self-support operation mode set upon power failure of the main AC power system, and a solar power generation apparatus.
2. Description of the Related Art
Solar power generation apparatuses are reconsidered as emergency power supplies in cases of disasters such as earthquakes. Such solar power generation apparatus comprises an inverter for converting DC electric power supplied from a solar cell into AC electric power and supplying it to consumer loads, and a switch for connecting the output from the inverter to a main AC power system such as a commercial AC power system or the like. When electric power supplied from the solar cell is insufficient for customer consumption power, the short electric power is received from the main AC power system; when electric power supplied from the solar cell exceeds customer consumption power, excess electric power is supplied to the main AC power system.
A control system of such inverter monitors the voltage waveform of the main AC power system, and ON/OFF-drives the individual switching elements of the inverter to obtain a voltage waveform corresponding to the instantaneous value and polarity of the voltage. In this inverter, when the main AC power system is cut off owing to a disaster, trouble, maintenance, or the like, a protection circuit immediately works to turn off the individual switching elements. Even when a breaker is used as the switch, the protection circuit works before the breaker opens. As a result, when the main AC power system has suffered a power failure or outage, the solar power generation apparatus itself fails to operate.
Therefore, in order to use the solar power generation apparatus using the inverter as an emergency power supply in disasters, the inverter must have a self-support operation function. For example, solar power generation apparatuses shown in FIGS. 6 and 7 are available. In FIGS. 6 and 7, reference numeral 1 denotes a solar panel built by a solar cell array; 2, an inverter; 3, a switch; 4, a consumer load; and 5, a main AC power system. Also, reference numeral 21 denotes a controller for the inverter 2; 22, an AC output switch; 23, an outlet for a self-support operation; and 24, a cord for connecting the outlet 23 and the consumer load 4.
In the system shown in FIG. 6, when the main AC power system 5 has suffered a power failure or outage, since the switch 3 is not always opened, as described above, if the self-support operation of the inverter 2 is inadvertently started, electric power is supplied to the main AC power system 5, and the inverter 2 may stop owing to an overload. Or the inverter 2 may cause an electric shock accident in the main AC power system 5. In order to solve these problems, the switch 3 must be manually opened, and thereafter, the self-support operation of the inverter 2 must be manually started.
In the system shown in FIG. 7, since the self-support operation outlet 23 alone of the inverter 2 can be used during the self-support operation, the load 4 to which electric power need be supplied must be brought to a position in the vicinity of the inverter 2 or electric power must be supplied to the load 4 via the cord 24.